General Discussion

Melorheostosis is a rare and progressive disease characterized by thickening or widening (hyperostosis) of the outer layers of the bone (cortical bone). Melorheostosis affects both bone and soft tissue growth and development. This disorder is benign (noncancerous), but it often results in severe functional limitation; chronic pain; malformed or immobilized muscles, tendons or ligaments; and limb, hand, or foot deformities.

Melorheostosis usually affects one particular segment of the appendicular skeleton (arms and legs). It is usually limited to one side of the body (rarely bilateral) and within a limb restricted to either the medial or lateral side of the bones. The disease can also affect the axial skeleton: pelvis, sternum, ribs and, more rarely, the spine and skull. Symptoms may progressively worsen over time.

In children, the condition usually presents with limb length inequality, deformity, or joint contractures. In adults, symptoms of pain, joint stiffness, and progressive deformity are more apparent.

The age of diagnosis is typically based on severity of onset and symptoms and varies widely in children and adults. Melorheostosis is usually observed in early childhood and may even be apparent in the first days of life. Fifty percent of patients with melorheostosis will develop symptoms by age 20.

Causes

Up to now the precise cause of melorheostosis is still unknown. In a small number of melorheostosis patients, a mutation in the LEMD3 gene has been identified. The LEMD3 gene codes for a protein that is part of the nuclear membrane. This membrane protein plays an inhibitory role in bone formation. However, the vast majority of sporadic patients with melorheostosis do not have a LEMD3 germline (egg or sperm) mutation. The current hypothesis is that melorheostosis is caused by a somatic mutation that is only present in the affected tissues. Mutations in the LEMD3 gene have also been associated with other bone disorders (osteopoikilosis or Buschke-Ollendorff syndrome).

Affected Populations

The estimated incidence of melorheostosis is 1 in 1,000,000. Both sexes are affected and approximately 400 cases have been reported.

Related Disorders

Symptoms of the following disorders can be similar to those of melorheostosis. Comparison may be useful for a differential diagnosis:

Osteopoikilosis is a rare and benign bone disorder characterized by multiple round or oval areas of increased bone density.

Buschke-Ollendorf syndrome is a rare hereditary disorder of connective tissue characterized by skin growths called connective tissue nevi and osteopoikilosis.

Linear scleroderma appears as a band-like thickening of skin on the arms and legs. It typically appears first during early childhood and is characterized by the failure of one limb to grow as rapidly as its counterpart.

Desmoid tumors commonly develop in the fibrous (connective) tissue of the body that forms tendons and ligaments, usually in the arms, legs or midsection, and also in the head and neck. Desmoid tumors can be invasive to surrounding tissues and difficult to control. (For more information on this disorder, choose “desmoid tumor” as your search term in the Rare Disease Database.)

Hemangiomas appear in early infancy and are growths made up of small blood vessels.

Scoliosis refers to side-to-side curvature of the spine. In the person with scoliosis, the spine may resemble an “S” rather than a straight line.

Diagnosis

In melorheostosis, bone scans appear to be markedly positive. However, on magnetic resonance imaging (MRI) there is usually a low signal. X-ray imaging is the preferred diagnostic tool for melorheostosis. X-rays often reveal a pattern of thickened bone (sclerotic bone lesions) that resembles dripping candle wax.

Standard Therapies

Treatment

Treatments are limited at the present time and are predominantly aimed at reducing symptoms. No treatment option has been found to be fully effective, and what may be helpful to one person may be ineffective or even detrimental to another. Treatment options may include surgery, physical and occupational therapy, hydrotherapy, and medications to alter the bone remodeling process.

Pain management may be challenging. Medications prescribed for pain may include non-steroidal anti-inflammatory drugs (NSAIDs),steroids or rarely narcotics. These medications are sometimes helpful in the early stages of the chronic progression of the disease but may be less so for the severely affected. However, some patients have shown benefit in either symptoms or on bone scans.

Investigational Therapies

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.

For information about clinical trials being conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Toll-free: (800) 411-1222

TTY: (866) 411-1010

Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:

NORD's Rare Disease Database provides brief introductions for patients and their families to more than 1,200 rare diseases. This is not a comprehensive database since there are nearly 7,000 diseases considered rare in the U.S. We add new topics as we are able to do so, with the help of rare disease medical experts.

If you are seeking information about a rare disease that is not in this database, we would suggest contacting the Genetic and Rare Diseases Information Center (GARD) at the National Institutes of Health. NIH has the most complete database of rare diseases in the U.S.

Representatives of patient organizations whose medical advisors are interested in assisting NORD in creating a report on a disease not currently covered in this database may write to orphan@rarediseases.org.